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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Physics and chemistry of minerals 27 (2000), S. 258-269 
    ISSN: 1432-2021
    Keywords: Key words Chlorites ; Iron lattice sites ; Mössbauer spectroscopy ; Molecular orbital calculations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Abstract  The different Fe2+ lattice sites in iron-rich chlorites have been characterized by Mössbauer spectroscopy and molecular orbital calculations in local density approximation. The Mössbauer measurements were recorded at 77 K within a small velocity range (±3.5 mm s−1) to provide high energy resolution. Additionally, measurements were recorded in a wider velocity range (±10.5 mm s−1) at temperatures of 140, 200, and 250 K in an applied field (7 T) parallel to the γ-beam. The zero-field spectra were analyzed with discrete Lorentzian-shaped quadrupole doublets to account for the Fe2+ sites M1, M2, and M3 and with a quadrupole distribution for Fe3+ sites. Such a procedure is justified by the results obtained from MO calculations, which reveal that different anion (OH−) distributions in the first coordination sphere of M1, M2, and M3 positions have more influence on the Fe2+ quadrupole splitting than cationic disorder. The spectra recorded in applied field were analyzed in the spin-Hamiltonian approximation, yielding a negative sign for the electric field gradient (efg) of Fe2+ in the M1, M2, and M3 positions. The results of the MO calculations are in quantitative agreement with experiment and reveal that differences in the quadrupole splittings (ΔE Q ), their temperature dependence and in the isomer shifts (δ) of Fe2+ in M1, M2, and M3 positions can theoretically by justified. Therefore, the combined Mössbauer and MO investigation shows that the three Fe2+ lattice sites in the chlorites investigated here can be discriminated according to their ΔE Q -δ parameter pairs. With the calculated average iron-oxygen bond strength, the MO study provides an explanation for the observed trend that the population of the three lattice sites by Fe2+ increases according to the relation M1 〈 M2 〈 M3.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2017-05-25
    Description: Rapidly star-forming galaxies adjacent to quasars at redshifts exceeding 6 Nature 545, 7655 (2017). doi:10.1038/nature22358 Authors: R. Decarli, F. Walter, B. P. Venemans, E. Bañados, F. Bertoldi, C. Carilli, X. Fan, E. P. Farina, C. Mazzucchelli, D. Riechers, H.-W. Rix, M. A. Strauss, R. Wang & Y. Yang The existence of massive (1011 solar masses) elliptical galaxies by redshift z ≈ 4 (refs 1, 2, 3; when the Universe was 1.5 billion years old) necessitates the presence of galaxies with star-formation rates exceeding 100 solar masses per year at z 〉 6 (corresponding to an age of the Universe of less than 1 billion years). Surveys have discovered hundreds of galaxies at these early cosmic epochs, but their star-formation rates are more than an order of magnitude lower. The only known galaxies with very high star-formation rates at z 〉 6 are, with one exception, the host galaxies of quasars, but these galaxies also host accreting supermassive (more than 109 solar masses) black holes, which probably affect the properties of the galaxies. Here we report observations of an emission line of singly ionized carbon ([C ii] at a wavelength of 158 micrometres) in four galaxies at z 〉 6 that are companions of quasars, with velocity offsets of less than 600 kilometres per second and linear offsets of less than 100 kiloparsecs. The discovery of these four galaxies was serendipitous; they are close to their companion quasars and appear bright in the far-infrared. On the basis of the [C ii] measurements, we estimate star-formation rates in the companions of more than 100 solar masses per year. These sources are similar to the host galaxies of the quasars in [C ii] brightness, linewidth and implied dynamical mass, but do not show evidence for accreting supermassive black holes. Similar systems have previously been found at lower redshift. We find such close companions in four out of the twenty-five z 〉 6 quasars surveyed, a fraction that needs to be accounted for in simulations. If they are representative of the bright end of the [C ii] luminosity function, then they can account for the population of massive elliptical galaxies at z ≈ 4 in terms of the density of cosmic space.
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
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  • 3
    Publication Date: 2020-02-12
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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  • 4
    Publication Date: 2020-02-12
    Description: The serpentine subgroup mineral berthierine was synthesized as a metastable precursor of the chlorite group mineral chamosite in cold seal pressure vessels at 575°C, 0.5 GPa and fO2-conditions of the NNO buffer from a glass of almandine bulk composition. The run products were investigated with X-ray powder diffraction (XRD), Mössbauer spectroscopy and electron microprobe analysis. One run product was also investigated by high-resolution transmission electron microscopy (HRTEM) and its heat capacity measured by heat pulse calorimetry and by differential scanning calorimetry in the temperature range 5-323 K. The XRD and HRTEM investigations clearly showed that the periodicity along the c axis of this sample is 7 A demonstrating that the serpentine subgroup mineral berthierine of composition (Fe1.832+Fe0.333+Al0.67)[Si1.33Al0.67O5](OH)4 has formed in the synthesis experiments. Integration of our heat capacity data, corrected to the composition (Fe2.5Al0.5)[Si1.5Al0.5O5](OH)4 for end-member berthierine, yields a standard entropy of 284.1±0.3 J mol-1K-1. The Cp polynomial Cp = 610.72 - 5140.0×T-0.5 - 5.8848×106 T-2 + 9.5444×108 T-3 is recommended for thermodynamic calculations above 298 K involving berthierine.
    Keywords: 550 - Earth sciences
    Type: info:eu-repo/semantics/article
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